On the latest installment of "Once Upon a Time," Zelena stole Regina's heart, and Snow discovered a painful secret from her past. 

In "Bleeding Through," viewers found out that Cora gave up baby Zelena because she was born out of wedlock, which cost her a royal wedding to Prince Leopold.

Belle (Emilie de Ravin) also spoke up to Regina (Lana Parrilla) about locking her away for all those years. Regina then sincerely apologizes, saying, "I'm sorry, Belle. I really, really am."

Later, after holding a botched seance, Regina and Snow (Ginnifer Goodwin) discover that Snow's mother, Eva, is responsible for their troubled history because Eva disgraced a pregnant Cora then took Leopold for herself.

The former enemies warm toward each other with Regina telling Snow she's sorry that her mother was not as good as she believed.

Also, Zelena (Rebecca Mader) has the Dark One take Regina's heart from Robin Hood (Sean Maguire). Snow then tells Regina that she has to share her love with Robin Hood. The talk inspires Regina to find Robin Hood, and the two share a passionate kiss.

Meanwhile, Zelena invites Rumple (Robert Carlyle) for a dinner, during which she tells him of his plan to enact her curse to turn back the clock so the Wicked Witch can kill Eva before she speaks to Leopold, which would endanger the futures of Snow, Emma and Regina.

Zelena plans to use the new Charming baby to enable time travel. Rumple feigns being impressed by her plan and goes in for a kiss. When he does, Zelena realizes his murderous agenda and keeps the dagger away from him then sends him back to his cage.

On the next episode, "A Curious Thing," "Zelena threatens to kill Henry if Hook — whose lips have been cursed by the Wicked Witch — doesn't proceed with kissing Emma, which will drain all of her magical powers away, and things begin to heat up between Regina and Robin Hood. Meanwhile, back in the Fairy Tale Land that was during the past year, Snow and Charming go in search of Glinda, the Good Witch of the South, to see if she can help them defeat Zelena, and the curse that will ultimately send the Fairy Tale characters back to Storybrooke is cast — but from an unlikely source."

Watch the promo below for "A Curious Thing," which airs Sunday, April 27 at 8 p.m. on ABC.